1. Technical Field
The subject matter described here generally relates to wind turbines, structures, and, more particularly, to expandable cable supports for wind turbines.
2. Related Art
A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by the machinery, such as to pump water or to grind wheat, then the wind turbine may be referred to as a windmill. Similarly, if the mechanical energy is converted to electricity, then the machine may also be referred to as a wind generator or wind power plant.
Wind turbines are typically categorized according to the vertical or horizontal axis about which the blades rotate. One so-called horizontal-axis wind generator is schematically illustrated in FIG. 1. This particular configuration for a wind turbine 2 includes a tower 4 supporting a nacelle 6 enclosing a drive train 8. The blades 10 are arranged on a hub to form a ‘rotor’ at one end of the drive train 8 outside of the nacelle 6. The rotating blades 10 drive a gearbox 12 connected to an electrical generator 14 at the other end of the drive train 8 arranged inside the nacelle 6 along with a control system 16 that may receive input from an anemometer 18.
The blades 10 generate lift and capture momentum from moving air that is them imparted to a rotor as the blades spin in the “rotor plane.” Each blade is typically secured at its “root” end, and then “spans” radially “outboard” to a free, “tip” end. The front, or “leading edge,” of the blade connects the forward-most points of the blade that first contact the air. The rear, or “trailing edge,” of the blade is where airflow that has been separated by the leading edge rejoins after passing over the suction and pressure surfaces of the blade. A “chord line” connects the leading and trailing edges of the blade in the direction of the typical airflow across the blade. The length of the chord fine is simply the “chord.”
“Angle of attack” is a term that is used in to describe the angle between the chord line of the blade 10 and the vector representing the relative motion between the blade and the air. “Pitching” refers to rotating the angle of attack of the entire blade 10 into or out of the wind in order to control the rotational speed and/or absorption of power from the wind. For example, pitching the blade “towards feather” rotates of the leading edge of the blade 10 into the wind, while pitching the blades “towards stall” rotates the leading edge of the blade out of the wind.
For so-called “pitch controlled” wind turbines, the pitch may be adjusted each time the wind changes in order to maintain the rotor blades at the optimum angle and maximize power output for all wind speeds. For example, the control system 16 may check the power output of the turbine 2 several times per second. When the power output becomes too high, the control system 16 then sends a signal to the blade pitch mechanism (not shown in FIG. 1) which causes the blades 10 to be pitched slightly out of the wind. The blades 10 are then turned back into the wind when the wind speed slows down.
Commonly-assigned U.S. Pat. No. 7,126,236 entitled “Methods and Apparatus for Pitch Control Power Conversion” is incorporated by reference here and partially reproduced in FIG. 2. The control system 16 (from FIG. 1) includes one or more controllers within control panel 112 for overall system monitoring and control including pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring.
The control system 16 provides control signals to the variable blade pitch drive or actuator 114 to control the pitch of blades 10 (FIG. 1) that drive hub 110. The drive train 8 (FIG. 1) of the wind turbine 2 includes a main rotor shaft 116 (also referred to as a “low speed shaft”) connected to hub 110 and a gear box 12. A high speed shaft from the opposite end of the gear box is used to drive a first generator 120. In some configurations, torque is transmitted via a coupling 122.
The blade pitch control signals are typically provided in the form of electrical impulses signals from the control system 16 that are carried along cables extending through a hole at the center of the shaft 116 from a slip ring attached to the back of the gearbox 12. However, the rotating shaft 116 can damage the external protective coating of the cables which can short circuit or otherwise interfere with the transmission of those control signals.